The instant invention is directed in general to optical systems in which a laser beam is injected into the end of an optical fiber and, more specifically, to laser based material processing systems in which a high power laser beam is injected into the fiber input end for transmission to a remote end of the fiber where material processing is performed with the emitted beam.
Laser based material processing as known in the art and as used herein, refers to performance of processes such as cutting, welding, drilling and soldering, using a continuous wave or pulsed laser beam. The average power of such a laser beam may range from as little as approximately one watt to 1000s of watts, the specific power being selected on the basis of the particular process being performed. It is known in the art to transmit the laser beam from the laser to the vicinity of the workpiece by means of an optical fiber. Apparatus and methods for injecting a laser beam into an optical fiber for transmission there through are disclosed in commonly assigned U.S. Pat. Nos. 4,564,736; 4,676,586; and 4,681,396 respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System", the disclosures of these patents being incorporated in their entirety herein by reference.
As disclosed in the above incorporated patents, injection of the laser beam into the fiber end is accomplished by focusing the beam, by means of one or more lenses, onto the prepared input end of the fiber. Specific requirements for the convergence of the focused beam cone, the beam spot size as focused on the fiber end, and the fiber end preparation are described in these patents. Compliance with these requirements is necessary in order to successfully inject the laser beam into the optical fiber for transmission there through. Implicit in these requirements is the need for the alignment of the focused laser beam to the optical fiber to be precise, in order to allow all or most of the laser radiation to enter the fiber core.
Perfect alignment is achieved when the plane defining the fiber tip is placed in the focus of the injected laser beam, or near the focal plane if the user determines such a position to be advantageous, and the fiber's longitudinal axis is centered on the transverse dimensions of the injected beam. Misalignment of the beam and fiber end will result in either inefficient or no beam transmission through the fiber. Where the laser beam has sufficient power, misalignment will result in damage to the fiber cladding or to the jacket surrounding the fiber cladding. Upon the occurrence of each need to replace a damaged optical fiber, the time required to effect fiber alignment with the beam injecting apparatus represents manufacturing downtime and therefore manufacturing cost and inefficiency. Furthermore, additional costs may be necessary in order to repair or replace any damaged optical fibers. Therefore, fiber injection must be completed without the high power beam damaging the fiber cladding or jacket during or after the alignment stage.
Various methods are known in the art for aligning optical components, such as the alignment of a single core optical fiber with a focused laser beam. Several methods are disclosed in commonly assigned U.S. Pat. Nos. 4,984,885; 4,840,450; and 4,739,162, respectively entitled, "Method and Apparatus for High Power Optical Fiber Injection and Alignment", "Apparatus and Method for Optical Fiber End Positioning for Laser Injection", and "Laser Beam Injecting System."
Such optical alignment methods include the use of cameras, microscopes, low power aligning lasers, infrared viewing of a high power laser operated at low, non-damaging power levels or some combination of these methods. However, most of the methods currently used to align focused beams with optical fibers only work well for low power laser beams. When these methods are used with high power beams the current methods fail to recognize that the incident beam may irradiate the fiber jacket or the cladding, which surround the fiber core, severely damaging these areas and rendering the fiber unusable.
Most current alignment methods are based on a "trial and error" approach. During a "trial and error" approach, the position of the optical fiber tip is adjusted by very small increments, often micrometers, while the laser source is incident upon the fiber. The fiber is manipulated until the beam is transmitted through the fiber core. However, during this manipulation, the incident radiation illuminates the areas surrounding the fiber core including the cladding, which is often made of silicone or doped glass, and the fiber jacket, which is often made of nylon or other organic polymers. The illumination of these unprotected and vulnerable areas often initiates catastrophic failure of the optical fiber tip.
Other methods of laser to fiber alignment utilize a variable attenuator to reduce the laser power below the damage threshold during alignment. Once alignment is accomplished, the attenuation is reduced and the full power beam is launched through the optical fiber. However, the use of a variable attenuator creates additional problems. Attenuators often fail to maintain the identical beam position over the attenuation range required, causing the transmitted beams to wander as the laser power is increased. This makes the use of attenuators in alignment methods unreliable for obtaining an accurate and reliable laser to fiber alignment.
Furthermore, a laser to fiber alignment method should be only moderately difficult to set up and maintain, such that factory personnel with little or no optical training would be fully capable of properly aligning the laser beam with the optical fiber.
Therefore, it is apparent from the above that there exists a need in the art for an apparatus and method for high power laser-to-fiber alignment, which is non-destructive to the fiber cladding and jacket. By remaining non-destructive, this apparatus and method will achieve alignment while maintaining the integrity of the cladding and the fiber jacket. Furthermore, it is apparent from the above that there also exists a need in the art for an apparatus and method for high power laser-to-fiber alignment which does not allow beams to wander during the alignment process, making it possible to obtain an accurate and reliable alignment. It is a purpose of this invention, to fulfill these and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.